1. Field of the Invention
The invention relates to a pulse-compression-type MTI doppler radar system capable of operating at a high prf and not introducing range ambiguities. More particularly, the invention relates to apparatus for transmitting a train of pulses alternately coded with at least two codes, auto-correlating the target return of each coded pulse with pulse compressors matched to each code, and processing the pulse-compressed target returns with at least two MTI processing channels each of which will process target returns from one range segment of the operable radar range.
2. Description of the Prior Art
In pulse-compression MTI doppler radar systems the prf at which pulses are transmitted is an important parameter. On one hand, it is desirable to have a long time interval between pulses, since a transmitted pulse must have the opportunity to travel to and from a target before another pulse is transmitted or ambiguities in target range result. On the other hand, it is desirable to have a short time interval between pulses since this increases the upper limit of the target blind speed. The target blind speed determines the maximum target speed that can be detected without target speed ambiguity.
The typical pulse-compression MTI doppler radar system in the prior art is composed of a prf generator, a wave-form generator, a transmitter, an antenna, a receiver, a pulse compressor, an MTI processor, and a display. Such a system is constrained by the above-described prf tradeoff. Methods of resolving the tradeoff exist such as transmitting pulse bursts at various prfs and using the Chinese remainder theorem. It is also known in prior art not involvng pulse-compression radar systems to sequentially transmit several double sideband waveforms separated in frequency so that ranges may be separated. In the receive mode the ranges are separated by filtering the sidebands appropriately. However, for a number of reasons these solutions have proved unsatisfactory. What is needed is an improved pulse-compression MTI doppler radar system capable of operating at a high prf to maintain a high upper limit on target blind speed, and yet still be capable of operating without range ambiguities at the operable radar range.